Building energy-saving potential of a dual-functional solar heating and radiative cooling system

Space heating and cooling devices that rely on renewable resources are in demand amid energy crises in parts of the world. However, common renewable space heating and cooling devices are mono-functional. For regions with heating and cooling seasons, using two mono-functional devices might double the installation and maintenance costs, and prolong the payback period. This study proposed a dual-functional renewable heating and cooling device by utilising solar power and nocturnal radiative cooling. The device is a modified solar heating (SH) collector that optimises the nocturnal radiative cooling (RC) to become an SHRC collector. Investigation of the SHRC collector's performance and energy-saving potential of a building-integrated SHRC collector was conducted using CFD and EnergyPlus. Analysis of the SHRC collector's performance in various environmental conditions shows that the SHRC collector can reach 42 % thermal efficiency at zero-reduced temperature and > 50 W/m(2) of net cooling power. Also, studies on the optimal air duct and air gap height reveal that a 1 cm air duct and 4 cm air gap as the best options for the SHRC collector design. Simulations of the building-integrated SHRC with a collector area of 9.43 m(2) for a typical 100 m(2) house building demonstrate the multi-seasonal advantage of the SHRC collector, with at least 1.5 kWh more daily savings than the SH and RC collectors in typical winter and summer days. Furthermore, the simulations estimate the annual combined heating and cooling energy savings by the SHRC collector around 32.7 % in Madrid, 25.5 % in Tokyo, and 14.0 % in Isfahan.